Embodiments of the present invention relate generally to an ionization system, and more particularly, to an ionization system with closed loop feedback and interleaved periods of sampling to determine upstream charge on an object and to determine a condition of the ionization system.
Air ionization is an effective method of eliminating static charges on target surfaces. Air ionizers generate large quantities of positive and negative ions in the surrounding atmosphere that serve as mobile carriers of charge in the air. As ions flow through the air, they are attracted to oppositely charged particles and surfaces. Neutralization of electrostatically charged surfaces can be rapidly achieved through this process.
Air ionization may be performed using electrical ionizers, which generate ions in a process known as corona discharge. Electrical ionizers generate air ions by intensifying an electric field around a sharp point until the field overcomes the dielectric strength of the surrounding air. Negative corona discharge occurs when electrons are flowing from the electrode into the surrounding air. Positive corona discharge occurs as a result of the flow of electrons from the air molecules into the electrode.
Ionizer devices, such as an alternating current (AC) or direct current (DC) charge neutralizing system, take many forms, such as ionizing bars, air ionization blowers, air ionization nozzles, and the like, and are utilized to neutralize static electrical charge by emitting positive and negative ions into the workspace or onto the surface of an area. Ionizing bars are typically used in continuous web operations such as paper printing, polymeric sheet material, or plastic bag fabrication. Air ionization blower and nozzles are typically used in workspaces for assembling electronics equipment such as hard disk drives, integrated circuits, and the like, that are sensitive to electrostatic discharge (ESD).
In a typical closed loop ionization system for conveyed materials (e.g., webs or the like), sensors are located downstream from the ionizer device. These sensors, typically electrostatic field meters or the like, evaluate residual charge on the material and a feedback signal is returned to the ionization system to drive the residual charge to zero, or as close to zero as possible. In these systems the downstream residual voltage is well characterized by information from the feedback sensor. The actual voltage on the conveyed material coming into the ionization system, i.e., the upstream voltage, is unknown. This information is important for safety and process control.
To determine the upstream voltage, an additional sensor located upstream of the ionizer device is necessary. This adds to the expense of the system, but more importantly, the charges on the conveyed material upstream of the ionizer device may be high (e.g., 10 kV or higher) and beyond the capabilities of standard charge sensors.
In addition, over time, an ionizer may accumulate debris. In order to maintain optimal performance of the ionizer, it is necessary to clean the ionizer in order to remove the debris. As an ionizer accumulates debris, the ionizer's charge will decrease and, therefore, the current flowing from the voltage supply into the ionizer will also decrease. A method for having the ionization system self-calibrate and indicate performance is described in U.S. Pat. No. 8,039,789 (Gorczyca, et al.), the entire contents of which are incorporated by reference herein. However, the method requires the initial accumulation of calibration data for a plurality of operating states of the high voltage power supply. Real-time data, in particular a sum of the current output to the positive and negative ionizers, acquired during operation is then compared to the closest data point to determine a difference in performance. The accumulation of calibration data for what may be 250 or more data points can be time consuming, and requires a large memory space to store the necessary baseline table.
It is desirable to provide an ionization system that can provide closed loop feedback and estimate upstream charge without the need for an additional upstream sensor.